This invention relates generally to propulsion systems and, more particularly, to an engine mounting assembly for a marine propulsion system.
Mechanical propulsion systems for propelling watercraft generally are classified as either outboard systems or inboard systems. Outboard systems typically are characterized by an outboard motor mounted to a vertical transom plate located on an outside stern of a boat hull. A propeller drive unit is attached to the motor, or powerhead, and extends from the powerhead into the water to generate thrust and propel the watercraft. Outboard motor systems are versatile, compact, and cost-effective units that are relatively easy to install on the boat hull. Also, because the outboard system is attached to the outside of the hull, the outboard motor system generally does not occupy interior space of the boat hull. However, due to structural constraints of the vertical transom plate mounts of outboard systems, watercraft with outboard systems are typically limited to certain motor capacities within size and weight constraints.
Inboard systems are typically characterized by larger, complicated, and relatively expensive engines in comparison to outboard systems. Inboard system engines are mounted in an engine compartment in a boat hull interior, and a drive unit, or stern drive, extends through a vertical wall of the boat hull into the water to generate thrust and propel the watercraft. Inboard systems, however, are much more complicated to install in a boat hull, which further increases the cost of a watercraft. Furthermore, bulky inboard engines and engine compartments often occupy a substantial amount of interior hull space due to the proximity of the engine compartment to a running surface of the hull.
In an exemplary embodiment of the invention, a steering arm yoke and trunnion assembly for a marine propulsion system includes a steering arm and a yoke including integral fluid paths for trim actuator fluids and for engine cooling water. The steering arm and yoke include a drum for rotating an attached propeller drive unit. The fluid paths extend through the drum, which is rotatably mounted to an upper unit of a marine propulsion system. The yoke includes pivot arms for attachment to a trunnion that includes actuator brackets for trim actuators fluidly connected to the actuator fluid paths of the drum.
In an exemplary embodiment, the steering arm yoke and trunnion assembly is part of a marine propulsion system including an outboard propulsion system powerhead mounted to a horizontal mounting plate in an outside engine compartment formed in a platform extending from a boat hull. The engine compartment is enclosed by an engine cover at a stern of a watercraft. The marine propulsion system includes an upper unit that includes the powerhead and a lower unit that includes a propeller drive unit. A four point mounting assembly eases installation of the upper and lower units and absorbs vibration of the upper and lower units to produce smooth, quiet propulsion of a watercraft. The outboard powerhead is mounted stationary to the horizontal mounting plate, and the steering arm yoke and trunnion assembly is attached to the horizontal mounting plate and extends outside of the boat platform to maneuver the watercraft.
The steering arm is connected to the yoke and includes the drum that extends through the stationary horizontal mounting plate. The steering arm rotates the drum and the attached propeller drive unit about a longitudinal axis through the drum. In response to operator input, the steering arm rotates the propeller drive unit to vary the orientation of the propeller relative to the boat platform, thereby allowing the boat to be steered.
The yoke also allows the propeller drive unit to pivot about a pivot pin toward and away from the platform to adjust a trim and tilt of the propeller drive unit relative to the platform. The yoke includes integral fluid paths for hydraulic fluids to power hydraulic cylinders coupled to the yoke to pivot the propeller drive unit, and includes integral fluid paths for powerhead cooling water. A universal joint rotatably couples a powerhead drive shaft to a propeller drive unit gearcase shaft and is surrounded by a bellows to facilitate pivoting of the propeller drive unit and to protect the universal joint. The bellows extends from a bottom of the steering arm to a trunnion that is attached to a propeller drive unit gearcase.
The marine propulsion system upper and lower units, including outboard powerhead, the mounting assembly, the steering arm yoke and trunnion assembly, gear shift mechanism, gearcase, and propeller, are fully pre-assembled and tested, and the assembly is lowered through a recess in the boat platform. The horizontal mounting plate is secured horizontally to the platform above a running surface of the hull, i.e., above the water line when the boat is idly afloat in the water. Installation is completed by making hydraulic connections for trim, tilt, and steering of the propeller drive unit, and by making appropriate fuel, electrical and control system connections to the various components of the propulsion system.
Thus, the steering arm yoke and trunnion assembly facilitates a marine propulsion system that provides the versatility, compactness and cost savings of an outboard powerhead with the stability and performance advantages of an inboard system. Structural limitations and instability of vertical transom plate mounts are avoided by mounting the outboard powerhead to the horizontal mounting plate in the boat platform.